(1) Field of the Invention
This invention relates to a composition which comprises three materials: a biobased biodegradable polymer, a polylactic acid (PLA) or polyhydroxybutyrate (PHB), a petroleum-based biodegradable polymer (poly-(butylene adipate-co-terephthalate) (PBAT), and a fatty acid triglyceride quaternary ammonium salt modified nanoclay to develop a high-barrier, biodegradable material for packaging. The composition is formed by reactive blending, particularly extrusion.
(2) Description of Related Art
The exponential growth of the use of polymeric materials in everyday life has led to the accumulation of huge amounts of non-degradable waste materials across our planet. This growing threat to the environment has led to research in biodegradable materials as replacement for non-degradable, commonly used materials.
High barrier packaging is the most needed polymeric material for today's food industries. High barrier may be defined as “any material that is capable of preventing the ingress of another material, whether it is gas (mostly oxygen and water vapor) or flavor or aroma”. High barrier packaging can comprise several layers (3 to 6 plastic layers or more) and various types of polymer films which provide properties such as extended shelf life for foods, cosmetics and pharmaceuticals.
The preferred methods of making high barrier packaging are: co-extrusion, lamination and coating. Problems, including de-lamination and migration, can lead to diffusion of toxic substances into food, and loss of package integrity, which results in loss of the food.
This invention uses biobased biodegradable polymers such as poly L-Lactide acid (PLLA) or polyhydroxybutyrate (PHB). These polymers have high stiffness and low elongation with high brittleness and can not be used to form films or flexible articles. Polylactic acid (PLA) is a stiff, rigid thermoplastic derived from renewable resources (like corn) and can be totally amorphous or semi crystalline in nature depending on the stereo purity of the polymer backbone (D. Garlotta, J. Polymers and the Environment, Vol. 9, No. 2, April 2001, 63-84). PHB is an enantiomerically pure polymer with a methyl substituent regularly along the backbone adjacent to the repeating methylene unit. (A. Fiechter, Plastics from Bacteria and for Bacteria: Poly (B-Hydroxyalkanoates) as Natural, Biocompatible, and Biodegradable Polyesters, Springer-Verlag, New York, 1990, p. 77-93). The structure of PHB is comparable with that of isotactic polypropylene (PP) and hence it has many similar properties like PP. The isotacticity combined with the linear nature of the chain results in a highly crystalline material with very attractive strength and modulus but very poor elongation.
Researchers have investigated the blending of hard polymers with tough polymers to achieve optimized properties and performances (U.S. Pat. No. 6,573,340 to Khemani et al; U.S. Patent Appln. No. 20030166748 to Khemani et al and U.S. Patent Appln. No. 20030166779 to Khemani). Blends of PLA with some biodegradable polymers such as poly(butylene succinate), poly-ε-caprolactone and PBAT have been reported (U.S. Patent Appln. No. 20020052445 to Terada et al; U.S. Pat. No. 5,883,199 and U.S. Pat. No. 6,787,613 to Bastioli et al). Similarly, PHB blends with biodegradable polymers like poly(butylene succinate), poly-ε-caprolactone, poly(ethylene glycol) and poly(ethylene oxide) have been reported (Y. Kumagai and Y. Doi, Polymer Degrad. Stab. 36 (1992). 241; F. Gassner and A. J. Owen, Polymer 35 (1994) 2233; M. Gada, R. A. Gross and S. P. McCarthy, in Biodegradable Plastics and Polymers,” edited by Y. Doi and K. Fukuda (Elsevier Science B. V. 1994); X. Shuai, Y. He, Y. Na, Y. Inoue., J. of App. Poly. Sci., 80, 2600-2608 (2001); Z. Qui, T. Ikehara, T. Nishi, Polymer 44 (2003) 2503-2508; B. Immirzi, M. Malinconico, G. Orsello, S. Portofino, M. G. Volpe, J. Mat. Sci., 34 (1999) 1625-1639 and Y. Na, Y. He, N. I. Asakawa, N. Yoshie and Y. Inoue, Macromolecules 2002, 35, 727-735).
Development of polymer/clay nanocomposites (PCN's) is one of the latest examples in evolution of materials of superior properties as compared to their virgin forms (Giannelis, E. O., “Polymer layered silicate nanocomposites”, Advanced Materials 8, 2935 (1996); Okada, O., Kawasumi, M., Usuki, A., Kurauchi, T., Kamigaito, O., Mater. Res. Soc. Symp. Proc. 171, 45 (1990); U.S. Pat. No. 5,747,560 to Christiani et al; Pinnavaia, T. J., Lan, T., Wang, Z., Shi, H., Kavaratna, P. D. ACS Symp. Ser. 622, 250 (1996); S. S. Ray, K. Yamada, M. Okamoto, K. Ueda, “New polylactide-layered silicate nanocomposites. 2. Concurrent improvements of material properties, biodegradability and melt rheology”, Polymer, 44, 857 (2003); S. Ray et al., “Novel Porous Ceramic Material via Burning of Polylactide/Layered Silicate Nanocomposite”, Nanoletters, 2, 423 (2002); P. Maiti et al., “Renewable Plastics: Synthesis and Properties of PHB Nanocomposites”, Polym. Mater. Sci. Eng., 88, 58-59 (2003); H. Park et al., “Environmentally Being Injection Molded “Green” Nanocomposite Materials from Renewable Resources for Automotive Applications”, 18th Annual Conference of American Society for Composite, 2003; and Alexandre, M. et al., “Polymer-layered silicate nanocomposites: preparation, properties and uses of a new class of materials”, Mater. Sci. Eng. R: Reports, 28, 2). The incorporation of nanosize clay platelets into a material significantly decreases the permeation rate of penetrants through a polymer matrix by increasing the penetrant tortousity. Nanocomposites show increase in heat distortion temperature, dimensional stability, improved barrier properties, flame retardancy, and enhanced physico/thermo-mechanical properties over conventional polymers (Giannelis, E. P. et al., “Polymer-Silicate Nanocomposites: Model Systems for Confined Polymers and Polymer Brushes”, Adv. Polym. Sci., 138, 107; Gilman, J. W. et al., “Flammability Properties of Polymer-Layered-Silicate Nanocomposites. Polypropylene and Polystyrene Nanocomposites”, Chem. Mater., 12, 1866; Messersmith, P. B. et al., Chem. Mater. 6, 1719, (1994); Yano, K. et al., Polymer Science Part A: Polymer Chemistry, 31, 2493, (1993); Vaia, R. A. et al., Chem. Mater., 5, 1694 (1993); Wang, Z. et al., Chem. Mater. 10, 3769, (1998); Ke, Y. et al., Applied Polymer Science, 71, 1139, (1999) and Hasegawa, N. et al., J. Applied Polymer Science, 63, 137, (1997)). Polymer-clay nanocomposites are achieving rapid growth in packaging, even more than in automotive applications. Nanoclay technologies can improve a packaging material's oxygen-, carbon dioxide-, moisture- and odor-barrier characteristics.
Based on extensive examination of the literature, the following problems were identified with conventional high barrier packaging polymers:                (1) Non-biodegradable food packaging materials end up as municipal waste leading to environmental waste problems.        (2) Rising landfill costs and decreasing landfill space.        (3) Incineration leads to a net contribution to atmospheric CO2.        (4) Conventional polymeric packaging is based on non-renewable resources and hence are not sustainable or eco-friendly and which leads to a need for alternative eco-friendly green materials that can replace these non-renewable-resource based non-biodegradable materials.        (5) Multilayer high barrier films have problems with delamination and high processing costs.        (6) Metallized coatings can not biodegrade nor be incinerated.        